Electromagnetic tachometer.



N. M. HOPKINS.

ELECTROMAGNETIC TACHOMETER.

APPLICATION FILED JAN. 19, 1911. 1,055,91 1. Patented Mar. 11, 1913.

2 SHEETS-SHEET 1.

C(Llrwo co: Ira/6:06am 7? 2M N. M. HOPKINS.

ELECTROMAGNETIC TACHOMETER.

APPLICATION FILED JAN.19,1911v 1,055,91 1. Patented Mar. 11, 1913.

Ia J2 SHEETS-SHEET 2.

UNITED STATES PATENT or uon.

NEVIL MONROE HOPKINS, OF WASHINGTON; DISTRICT OF COLUMBIA, ASSIG-NOR, BY

MESNE ASSIGNMENTS, TO THE ELECTRIC TACHOMETER COMPANY, OF PHILADEL- PHIA, PENNSYLVANIA, A CORPORATION OF NEW JERSEY.

ELECTROMAGNETIC TACHOMETER.

Application filed January 19, 1911. Serial No. 603,510.

To all whom it may concern:

Be it known that I, NEv'rL Mormon Hor- KINS, a citizen of the United States, residing at Washington, in the Districtof Columbia, have invented certain new and useful Improvements in Electromagnetic Ta chometers, of which the following is a specification. i

This tachometer comprises an indicating instrument having an electromagnet wound and connected to provide a rotating magnetic field, and a rotor in inductive relation thereto, carrying a pointer and movingagainst the pressure of a spring, and a source of alternating, preferably polyphase current, driven or controlled bythe wheel or shaft whose speed is to be measured.

Figure 1 is an axial section of the meter, on the'line I-I of F ig. 2 and of a magneto giving three-phase current and adapted to be driven by a gear on the wheel or shaft of a vehicle; Fig. 2 is a horizontal section onthe line IIII of Fig. 1; Fig.3 is a horizontal section on the line III-III of'Fig. 1; Fig. 4 is a side elevation of the rotor and electromagneticfield members, I separated; Fig. 5 is a plan view of the six-pole electromagnet, showing their windings connected for three-phase current; Fig. 6 is a vertical central section of commutating mechanism for converting direct battery current into three-phase alternating current, also .driving'an odometer and an electric contactmaker; and Fig. 7 is a developed plan of the commutator shown in Fig. 6. v

The indicating instrument comprises a case 1 having a glass front 2 and a dial 3,

graduated, e. 9., in miles per hour. Screwed to the bottom of the case is a disk 4, carrying a central tube 5 into which is screwed a plu 6 having a conical seat for the shaft 7 oftie rotor. Secured to this disk are osts 8 which carry an upper plate 9 containing a jeweled bearing 10 for the upper end of the rotor-shaft.

Centrally supported in the case is the electromagnet 11, consisting ofa series of superposed sheet-iron Eeces providing six radial pole-pieces 12. ach pole-piece carries a winding 13 and the six windings are connected as shown in Fi 5 to receive three-phase current througi leads l4 and provide a rotating magnetic field. Surrounding and spaced away from the ends of the pole-pieces is an iron ring 15, flanged outward at right angles from a disk 16 having a sleeve 17 revolubly mounted on the tube 5. This ring has six openings 18, corresponding in size to and arranged slightly' out of alinement with the pole-pieces-12. The ring serves as a path for the magnetic flux emanating from the pole-pieces, exce t where its continuity is interrupted by t e openings 18. The reluctance of this path increases as. the openings are brought more closely into alinement with the pole-pieces, by rotation of the ring. This fact is utilized to automatically compensate for the temperature-changes of resistance in the tachometer electric circuit, which comprises not only the electromagnet windings but also the instrument leads and the generator windings, or, alternatively, the commutator-brushes and segments and the battery.

For thispurpose, a bi-metallic strip '19- is.

tachometer thereby cause the thermostatic strip 19 to shift the iron ring 15 and bring its openings 18 more or less closely into alinement with the pole-pieces 12, the increased resistance of the electric circuit at higher temperatures being thereby automatically compensated by the decreased reluctance of the iron path 15, due to the shift- 'ing of the openings 18 to a position farther out of alinement with the ole-pieces.

The size and position 0? the openings 18 must be so predetermined andthe range of movement of the bimetallic strips 19 so adjusted for each instrument as to compensate for the temperature-changes in the tachometer circuit. Exact calibration of the speedscale at different temperatures therefore requires the use of the particular leads and source of current which, or the duplicates of which, are to be used in the particular tachometer combination.

The rotor consists of an inverted cup 23, preferably of aluminum, fixed on the shaft 7, its depending flange extending between the pole-pieces 12 and the ring 15, being traversed by the magnetic flux. The upper end of this shaft carries a pointer 24 indi- Patented Mar. 11, 1913.

- upon which bear brushes connected to the leads 14 of the indicating instrument. The armature is driven, through fine-toothed gears 31 within the case, by a counter-shaft 32 havin an external pinion 33 adapted to mesh wit a gear on the wheel of an automobile, or to be otherwise driven by the rotating member whose speed is to be indicated.

The alternative source of three-phase current illustrated in Fig. 6 comprises a water- .and dust-proof case 34, adapted to be mounted for example on the steeringknuckleof an automobile, in which is journaled a shaft 35 having an external pinion 36 adapted to mesh with a gear on the automobile-wheel. On this shaft is a commutator comprising an insulating drum 37 hearing two copper rings 38, 39, shown developed in Fig. 7.. Two brushes 40, 41, connected to an electric battery 42 through a circuit including a push-button 43, bear on the outer peripherally-continuous portions of the rings 38, 39, respectively. Three intermediate brushes 44, 45, 46 are arranged to bear, at different times, on the peripherallydiscontinuous portions of both rings, these rings being shaped and intermeshed as shown in Fig. 7 to convert the direct current of the battery into three-phase alternating current, which is likewise delivered to the leads 14 of the indicatinginstrument. An odometer 47 is mounted in the upper wall of the commutator case 34, being driven through gears 48, 49 by a worm 50 on the shaft 35. This worm also drives a lower pinion 51, the shaft of which carries a cam 52 adapted to intermittently tact-spring53 against a fixe contact 54 and thereby close an external electric circuit, for example that of an electromagnetioally-actuated odometer on the dash-board of the automobile. When commutated bat,- te -current is thus used to roduce the rt tatmg magnetic field, the in icator responds only when the push-button 43 is pressed,

thus minimizing the consumption of the current.

I claim:

1. A tachometer, comprising .an electromagnetic member wound to, provide a rotatmagnetic field, an indicator member in ihductive relation thereto, an armature havress a COI1-' ing portions of different reluctance adjacent to the poles of said electromagnetic member, thermostatic means for shifting said armature and thereby varying the magnetic flux through said indicator member, and means for supplying alternating current to said electromagnetic member, including a member driven by the Wheel or shaft whose speed is to be measured.

2. A tachometer, comprising an electromagnetic member wound to provide a rotating magnetic field, an indicator member in inductive relation thereto, means for varying the magnetic flux through said indicator member to compensate for temperaturechanges of resistance in the circuit of said electromagnetic member, and means for supplying alternating current to said electromagnetic member,, including a member driven by the wheel or shaft whose speed is to be measured.

3. A tachometer, comprising an electromagnetic member wound to provide a rotating magnetic field, an armature, an indicator member between said electromagnetic member and armature, means for varying the magnetic flux through said indicator member to compensate for temperature magnetic member, including a member driven by the wheel or shaft whose speed is to be measured.

4. A tachometer, comprising an electromagnetic member havin polyphase windings, an armature, an in icator member between said electromagnetic member and armature, means for varying the magnetic flux through said indicator member to compensate for temperature-changes of resistance in the circuit of said electromagnetic member, and means for supplying polyphase current to said electromagnetic member, including a member driven by the wheel or shaft whose speed is to be measured.

5. A tachometer, com rising an electromagnetic system, an in icator member in inductive relation thereto, means for supplying alternating current to said system, including a member driven by the wheel or shaft whose speed is to be measured, a thermostat, and means controlled by said thermostat for compensating temperaturechanges of resistance in the electric circuit of said tachometer.

6. In a'tachometer, comprising an electromagnetic member wound toprovide a rotating magnetic field, an armature, an india thermostat for compensating tem .eraturechanges of resistance in the electric circuit of Sazid tachometer.

7. In a tachometer, comprising an electromagnetic member ound to provide a rotating magnetic field, a movable armature having portions of different reluctance, an indicator member between said electromagnetic member and armature, and means for supply alternating current to said electromagneti: member, including a member driven by the wheel or shaft whose speed is to be measured, automatic means, including said armature and a thermostat ad "ipted to shift said armature, for compensating tempera turn changes of resistance in tha electric circuit of s id tachometer.

8. A tachometer, comprising an indicator member and a winding or windings adapted to receive electric current and actuate said indicator member, means for supplying electric current to said winding or windings, including a member driven by the wheel or shaft Whose speed is to be measured, a thermostat, and means controlled by said thermostat for compensating temperature changes of resistance in the electric circuit of said tachometer.

In testimony whereof, I aflix my signa ture in presence of two witnesses.

NEVIL MONROE HOPKINS.

Witnesses:

EUGENE A. BYRNES, Jos. H. BLAcKwoon. 

